Laser devices that amplify and output signal light with optical fiber amplifiers are widely known, for example as light sources for microscopes, shape measurement devices, exposure devices, and so on. The output wavelength of a laser device is determined according to the application and the function of the device to which it is to be installed, and an optical fiber amplifier is used that is doped with an excitation medium that corresponds to that output wavelength. For example, an erbium doped optical fiber amplifier (EDFA) in which a quartz optical fiber is doped with erbium (Er), an ytterbium doped optical fiber amplifier (YDFA) that is doped with ytterbium (Yb), and so on are known as optical fiber amplifiers (refer to Patent Document #1 and Patent Document #2).